Does any know how to active a game that I bought with other reseller (like amazon, etc...) in STEAM? Can you send me a link to list of game that steam support to do that? Any other pro and cons for that action? I want to ask since in amazon, there's alot better deal. But I want to put all my games in one place (for now, it's STEAM).

Go to the games tab, click 'activate a product on steam' read the information that comes up, agree to the user agreement after having read it then click the arrow to the next page, then type in the game code. I've added games this way. There's no cons to this action, as far as I can see, and in your Steam game purchase history the game will come up as retail. The only, potential, downside is that not all games can be redeemed on Steam. Make sure Amazon states that the DRM for the game includes Steam. Happy bargin hunting!

Help. I want to activate a game I have bough from external client. I've launched steam, logged in... but when I press the + ADD A GAME in the bottom left corner, nothing happens. What should I do? I am tryign to play Civ 5, and have the gamer key?